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Flashcards in deck_736622 Deck (60):
1

What does the P wave represent?Why is it a small upward depolarisation?

Atrial depolarisation Due to: smaller muscle mass and depolarisation moving towards the electrode

2

What does the QRS complex represent?

Ventricular contraction

3

What does Q represent?

Septal depolarisation spreading to ventricles

4

What does R represent?

Main ventricular depolarisation

5

What does S represent?

End of ventricular depolarisation

6

When does atrial repolarisation take place?

During the same time as ventricular depolarisation-- during QRS complex

7

What does the T wave represent?

Ventricular repolarisation

8

Describe the T wave shape

Upward signal as repolarisation is away from electrodeMedium sized as timing in the different cells is dispersed

9

What does the PR interval measure?

Time taken for impulse to reach ventricles from the SA node

10

What is a normal time for a PR interval?

0.12 to 0.2 seconds 3-5 small squares

11

What does a short PR interval indicate?

Atria have been depolarised close to the AV node or the is an abnormality of conduction from the atria to the ventricles.

12

What does the duration of the QRS complex represent?

How long excitation takes to spread through the ventricles

13

What is the normal duration of a QRS complex?

0.12 seconds or less

14

What does a widened QRS complex represent?

An abnormality of conduction through the ventricles E.g. Bundle branch block

15

What are the V leads?

Six chest leadsMade from 6 positions overlying the 4th and 5th rib spaces -- look in horizontal plane from the front and from the left

16

What do V1 and V2 show?

Right ventricle

17

What do V3 and V4 show?

Septum and anterior wall of left ventricle

18

What do V5 and V6 show?

Anterior and lateral walls of left ventricle

19

What is the cardiac axis?

The average direction of spread of the depolarisation wave from the front

20

Where can you deduct the cardiac axis?What is the normal shape?

From leads I, II and III Defects signal upwards as depolarisation is spreading towards the three leads

21

When does right axis deviation occur?What is it associated with?

When the right ventricle becomes hypertrophied. Usually associated with pulmonary condition putting a strain on the right side of the heart as well as congenital heart defects.

22

What do you see form the leads in right axis deviation?

Deflection in I becomes negativeDeflection in III becomes positive -- axis swings towards the right

23

When does left axis deviation occur?What is it usually due to?

When the left ventricle becomes hypertrophied Usually due to a conduction defect-- unlikely to be due to increased bulk of left ventricle

24

What do you usually see from the leads in left axis deviation?

QRS complex become negative in III Only is significant when QRS deflection is predominantly negative in lead II

25

What is first degree heart block?

Prolonged PR interval

26

What is first degree heart block a sign of?

Coronary artery diseaseAcute rheumatic carditisDigitalis toxicityElectrolyte disturbances

27

What is second degree heart block?

Erratic PR interval Excitations fails to pass through the AV node or the bundle of His

28

What are the causes of second degree heart block?

Same as first degree heart block: Coronary artery diseaseAcute rheumatic carditisDigitalis toxicityElectrolyte disturbances

29

What is third degree heart block?

Complete atrioventricular block-- atrial contraction is normal but no beats are conducted to the ventricles-- the two are disconnected electrically

30

How are the ventricles excited in third degree heart block?

By a slow escape mechanism

31

How can you recognise third degree heart block?

P wave rate is normal (90)QRS rate is low (36)No relationship between P and QRSAbnormal shaped QRS complexes due to abnormal spread of depolarisation from ventricular focus

32

What can cause third degree heart block?

Acutely -- transient heart attackChronically -- fibrosis around bundle of His

33

When can a right bundle brach block be normal?

When the duration of the QRS complex is normal

34

What do bundle branch blocks indicate?

RBBB indicates problems with the R side of the heartLBBB always indicates heart disease, usually on the L side

35

What changes occur in the ECG during right bundle brach block?

V1 lead -- normal R wave, second R wave due to failure of conduction pathway V6 lead -- smaller Q wave, normal R wave, wide deep S wave

36

What changes occur in the ECG during left bundle brach block?

V1 lead -- small Q, R wave (inspire of smaller mule mass), S wave (late depolarisation of LV)V6 lead -- R wave, S wave (appears as a notch), second R wave (due to late depolarisation of LV)

37

Where is right bundle brach block most easily seen?

In V1, where there is an RSR pattern

38

Where is left bundle brach block best seen?

In V6 where there is a "rabbit ears" pattern

39

Describe the branching of the bundle of His

From the AV node, two branches arise. The right bundle branch and the left bundle branch. The right bundle branch has no main divisions. The left bundle branch has two main divisions -- anterior and posterior fascicles

40

Which pacemaker cells have priority?

SAN pacemaker cells. They pre-empt other pacemakers due to a faster firing rate.

41

What can you use in order to determine the cardiac axis?

The lead with the smallest possible R wave which will be the lead at 90 degrees to the cardiac axis.

42

When analysing an ECG what do you look for?

RateRhythmAxis P waveP-R segmentQRS complexQ-T interval T wave

43

When is the P wave absent?

In atrial fibrillation

44

What are abnormalities that can be seen in the P-R interval?

First degree heart block = prolonged P-R intervalSecond degree heart block = erratic P-R interval Third degree heart block = no relationship between P and QRS complex

45

What is sinus rhythm?

Pacemaker cells in the SAN are controlling the heart rate -- normal depolarisation

46

What are the features of myocardial infarction?

ST elevationPathological Q waves -- greater than one small square across Inverted T waves

47

What changes from the MI are permanent?

Pathological Q waves are permament -- present in full thickness MI-- due to scar tissue forming which effectively blocks the circuit Inverted T waves

48

What do broader QRS complexes represent?

Escape rhythm-- ventricle is taking over as the pacemaker

49

Where can you see an inferior MI?Which coronary artery is likely to be responsible?

Leads II, III and aVfRight coronary artery

50

Where can you see an anteroseptal MI?Which coronary artery is likely to be responsible?

V1 and V2Left anterior descending coronary artery

51

Where can you see an anteroapical MI?Which coronary artery is likely to be responsible?

V3 and V4Distal left anterior descending coronary artery

52

Where can you see an anterolateral MI?Which coronary artery is likely to be responsible?

V5, V6, I, aVLCircumflex coronary artery

53

Where can you see an extensive anterior MI?Which coronary artery is likely to be responsible?

V1 - V6, I, aVLProximal left coronary artery

54

Where can you see a posterior MI?Which coronary artery is likely to be responsible?Wat are you likely to see in this case?

V1 and V2Right coronary artery ST depression in anterior leads or as tall R waves

55

Where is the MI if there are changes in leads II, III and aVf?

Inferior

56

Where is the MI if there are changes in leads V1 and V2?

Anteroseptal

57

Where is the MI if there are changes in leads V3 and V4?

Anteroapical

58

Where is the MI if there are changes in leads V5, V6, I and aVL?

Anterolateral

59

Where is the MI if there are changes in leads V1 - V6, I and aVL?

Extensive anterior

60

Where is the MI if there are tall R waves in V1 and V2?

Posterior aspect